Camshaft phasers (“cam phasers”) for varying the timing of combustion valves in internal combustion engines are well known. A first element, known generally as a sprocket element, is driven by a chain, belt, or gearing from an engine's crankshaft. A second element, known generally as a camshaft plate, is mounted to the end of an engine's camshaft.
U.S. Pat. No. 7,421,990 discloses an eVCP comprising first and second harmonic gear drive units facing each other along a common axis of the camshaft and the phaser and connected by a common flexible spline (flexspline). The first, or input, harmonic drive unit is driven by an engine sprocket, and the second, or output, harmonic drive unit is connected to an engine camshaft.
A first drawback of this arrangement is that the overall phaser package is undesirably bulky in an axial direction and thus consumptive of precious space in an engine's allotted envelope in a vehicle.
A second drawback is that two complete wave generator units are required, resulting in complexity of design and cost of fabrication.
A third drawback is that the phaser has no means to move the driven unit and attached camshaft to a phase position with respect to the crankshaft that would allow the engine to start and/or run in case of drive motor power malfunction. eVCPs have been put into production by two Japanese car manufacturers; interestingly, these devices have been limited to very low phase shift authority despite the trend in hydraulic variable cam phasers (hVCP) to have greater shift authority. Unlike hVCP, the prior art eVCP has no default seeking or locking mechanism. Thus, phase authority in production eVCPs to date has been undesirably limited to a low phase angle to avoid a stall or no-restart condition if the rotational position of the eVCP is far from an engine-operable position when it experiences eMotor or controller malfunction.
U.S. patent application Ser. No. 12/536,575 (parent to the present application), discloses an eVCP camshaft phaser comprising a flat HD having a circular spline and a dynamic spline linked by a common flexspline within the circular and dynamic splines, and a single wave generator disposed within the flexspline. The circular spline is connectable to either of an engine crankshaft sprocket or an engine camshaft, the dynamic spline being connectable to the other thereof. The wave generator is driven selectively by an eMotor to cause the dynamic spline to rotate past the circular spline, thereby changing the phase relationship between the crankshaft and the camshaft. The eMotor may be equipped with an electromagnetic brake. At least one coaxial coil spring is connected to the sprocket and to the phaser hub and is positioned and tensioned to bias the phaser and camshaft to a default position wherein the engine can run or be restarted should control of the eMotor be lost, resulting in the eMotor being unintentionally de-energized or held in an unintended energized position. In one aspect of the invention, the spring is contained in a spring cassette for easy assembly into the eVCP.
It has been shown that the HD as disclosed is well suited to operate satisfactorily under anticipated torque loading. However, a shortcoming of the disclosed invention is that if the HD is exposed to radial loading or bending, loading the splines within, the HD may become overstressed, causing the flex spline surface to yield, potentially leading to binding of the gear reducer.
What is needed in the art is an eVCP including means for increasing housing radial support for the journal bearing and the HD to control housing distortion due to input loading. Preferably, such support provided without increasing the housing bulk.
It is a principal object of the present invention to minimize housing distortion of an eVCP from radial loading or bending loading.